Offgases containing volatile organic carbon are generated in many different industrial processes. One of such processes involves the production of aluminum alloy sheet and foil by passing an aluminum alloy body through sets of metal rolls while spraying a rolling mill coolant, typically containing a light mineral oil, onto the aluminum alloy body as it passes through the mill. Alternatively, the coolant may be an emulsion comprising about 5-10 wt. % mineral oil. Heat produced from the rolling process vaporizes some of the rolling mill coolant thereby generating an oil fume which enters the atmosphere surrounding the mill. This oil fume consists mostly of mineral oil vapor combined with some oil mist. When the coolant is an emulsion, the fume contains a substantial amount of water vapor.
Several conventional methods are available for controlling volatile organic carbons in industrial offgases. A first method involves a centrifugal separator for removing only the oil mist particles which generally constitute approximately 10-30 wt % of the oil fume from the mill. A second method involves a carbon absorption bed to remove vapor only. In the carbon absorption bed process, any oil mist particles must first be removed to avoid wetting and "poisoning" the carbon. Otherwise, the oil mist deactivates the carbon bed when it is coated by the oil mist by wetting the carbon absorbent. A third method involves absorbing the oil fume in heavy oil. The oil then is vacuum distilled several times to separate the light mineral oil from the heavy oil.
These conventional methods for controlling volatile hydrocarbons from industrial processes have serious drawbacks making them less than entirely suitable for their intended purpose. The centrifugal separate method suffers from a low overall removal efficiency and does little to remove oil vapors in the fume from the rolling mill. The carbon absorption bed method has severe difficulty in operating on fumes containing even small amounts of oil mist, and the heavy oil absorption method is expensive to install and operate.
A principal objective of the present invention is to provide a process for scrubbing an industrial offgas, which process results in the formation of an oil-in-water microemulsion. Because microemulsions are thermodynamically stable, the process is capable of being operated at relatively high efficiency and at satisfactory cost.
A related objective of the invention is to provide a process for removing oil mists and oil vapors generated from rolling mills in the production of aluminum alloys sheet or foil.
Additional objectives and advantages of tile present invention will become apparent to persons skilled in the art from the detailed description that follows.